Conventional parallel kinematics robots comprise a plurality of drive arms each connected, directly or via a gearbox, to a respective shaft of a servo motor at one end. At the opposite end the drive arms are attached to a proximate end of rods via ball joints having three degrees of freedom (DOF). The rods transmit the rotating movement of the drive arms to a respective movement of an end effector that is attached to a distal end of the rods via ball joints. The servo motors and the respective drive arms are thereby working in parallel in the sense that manipulation of one drive arm does not affect the position of the remaining drive arms.
A delta robot is one well known type of parallel kinematics robot that can comprise three drive arms. Each drive arm is connected to an end effector with two rods having a ball joint at each end. The drive arms rotate about respective servo motor axes, the servo motors being arranged symmetrically such that their axes intersect at 60 degrees angles. Because the drive arms of a delta robot are relatively long and point in different directions the robot construction needs a lot of space. U.S. Pat. No. 7,188,544 discloses one type of a delta robot comprising three drive arms. Delta robots can also comprise four or more drive arms.
WO200366289 discloses other and less well known types of parallel kinematics robots comprising three or more drive arms. The robots according to WO200366289 differ from delta robots in that the rotational axes of the drive arms are parallel, and in many embodiments the drive arms even have one common rotational axis. The number of rods between the drive arms and the end effector vary from one to three depending on a drive arm and a robot embodiment. Also the drive arms of the robots according to WO200366289 need to be relatively long and well spread, and consequently need a lot of space.
Common for the both aforementioned parallel kinematics robot types is that the rods between the drive arms and the end effector are designed to be exposed to axial forces only. The necessary stiffness of the robots is obtained by spreading out the rods. As a consequence the conventional parallel kinematics robots cannot compete with SCARA robots in many applications because of their relatively poor accessibility and large space requirement.